Low profile high performance integrated antenna for small cell base station

ABSTRACT

The present disclosure relates to antenna design for Installation on small cell base stations. The antenna design corresponds to a conformal antenna design that fits into a traditional sun-shield of an outdoor base station. In another aspect, the antenna design supports multiple hands and multiple technologies. In a further aspect the antenna design provides a gain pattern that allows installation of the small cells into directional sectors to further enhance the spectral efficiency while providing a single installation location. In still a further aspect, the design permits the form factor of the base station to meet unique and desirable aesthetic principals such as a modem curved surface and an attractive and distinctive height, width and depth ratio.

This application is a U.S. National Stage Filing under 35 U.S.C. 371from International Application No. PCT/IB2014/001369, filed Mar. 12,2014 and published in English as WO 2014/177930 on Nov. 6, 2014, whichclaims the benefit of priority to U.S. Provisional Patent ApplicationSer. No. 61/794,681, filed Mar. 15, 2013, each of which is incorporatedherein by reference in its entirety.

BACKGROUND

Small cell base stations typically correspond to single sectorstand-alone base stations housed in a single enclosure. Small cell basestations convert internet protocol backhaul communications links into RFtransmit signals and converts RF receive signals into internet protocolbackhaul communications links. Small cell base stations often supportmultiple air interface technologies and enable high capacity datathroughput over a generally smaller coverage area relative to otherinfrastructure equipment. For example, the coverage area of a small cellcan have a range of less than 500 meters.

SUMMARY OF THE INVENTION

The present invention provides an antenna assembly for use in a smallcell base station, the antenna assembly comprising a housing having anexterior and an interior with an interior shape, a dielectric materialwithin the housing and conforming to the interior shape of the housing,a plurality of antenna patches positioned between the housing and thedielectric material and electric field polarizations for exciting eachof the plurality of antenna radiator patches. The housing may be aradome, which may function in part as a solar shield. The radome may bea curved radome. Each of the plurality of antenna patches may be locatedin thin pockets of the dielectric material. The plurality of antennapatches includes resonating and radiating patches, comprising a firstpair of elements for receiving in a frequency band for an LTE signal, asecond pair of elements for transmitting in a frequency band for an LTEsignal and a third pair of elements for operation in a Wi-Fi signalfrequency band. Each of the pairs of elements has a similarcross-polarization scheme and a similar gain pattern in vertical andazimuth directions. The antenna assembly may be located in a small basestation having cooling fins, wherein the cooling fins are removed behindthe plurality of antenna patches.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisdisclosure will become more readily appreciated as the same becomebetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram of the small cell base station.

FIG. 2 illustrates an embodiment of an antenna assembly for utilizationin a small cell base station.

FIG. 3 is an embodiment of the antenna assembly of FIG. 2 illustratingcomponents of the antenna assembly based on removal of an externalradome.

FIG. 4 is an embodiment of the antenna assembly of FIG. 2 illustrating areverse side of the antenna assembly.

FIG. 5 illustrates an embodiment of small cell base station features tomate with and utilize an antenna assembly.

FIG. 6 illustrates RF radiation patterns and orientations illustrativeof usage of an antenna assembly.

DETAILED DESCRIPTION OF THE INVENTION

Generally described, the present disclosure relates to antenna designfor installation on small cell base stations. In one aspect, the antennadesign corresponds to a conformal antenna design that fits into atraditional sun-shield of an outdoor base station. Dimensions of oneaspect of small cell base station are 575 mm height, 225 mm wide, 85 mmdeep. In another aspect, the antenna design supports multiple bands andmultiple technologies. Such an antenna design may be capable ofextending the bandwidth beyond what is usually possible with patchantennas. In a further aspect, the antenna design provides a gainpattern that allows installation of the small cells into directionalsectors to further enhance the spectral efficiency while providing asingle installation location. In still a further aspect, the designpermits the form factor of the base station to meet unique and desirableaesthetic principals such as a modern curved surface and an attractiveand distinctive height, width and depth ratio.

One skilled in the relevant art will appreciate that the disclosedembodiments and examples are illustrative in nature. Accordingly, thedisclosed embodiments and examples should not be construed as limiting.Additionally, although various aspects of the present disclosure havebeen identified and may be described together, the present disclosure isnot limited to embodiments in which all the identified aspects must beconsidered or combination of any described aspects should be required.

FIG. 1 is a block diagram of a small cell base station (110) or “smallcell.” A small cell base station is used to provide additional datathroughput to mobile units (150) by means of heterogeneous networkswhere the small cell may have overlapping coverage with one or morelarger macro base stations in the heterogeneous network. Additionally,small cell base stations may be configured to provide coverage of adense area of users, often referred to as a hot spot. In an embodiment,a small cell base station may be configured to implement, or otherwisesupport, multiple radio access networks or air interface technologieswithin a single unit. For example, a small cell may be configured toimplement one or more air interface standards promulgated bystandards-based organizations, such as 3GPP and 3GPP2 (i.e., 1×RTT,EVDO, WCDMA, HSPA, LTE, LTE-A, WiMAX, and the like). Air interface,standards and methodologies that use spectrum requiring a governmentalagency license which provides exclusive use of that spectrum, such asthe above described examples, are generally referred to as licensedtechnologies. Additionally, the small cell may also be configured toimplement one or more additional air interface standards promulgated bya standards-based organization, such as the IEEE (i.e., one or more ofthe IEEE 802.11a,b,g,n, or ac air interface standards). Air interfacestandards using spectrum not requiring an exclusive license bygovernmental agencies, such as the above described example, aregenerally referred to as unlicensed technologies.

The illustrative small cell base station implements an IP backhaulcomponent to provide communication to the core network. The IP backhaulcomponent may incorporate either a wired Ethernet connection (copper oroptic fiber) or a wireless backhaul (microwave or Wi-Fi). With continuedreference to FIG. 1, because of the compact size and the need to mountthe base station in discreet and an aesthetically pleasing manner, it isadvantageous to provide integrated antennas (155, 195) within thehousing that are not conspicuous but also provide superior performance.

FIG. 2 illustrates an embodiment of an antenna assembly for utilizationin a small cell base station. As illustrated in FIG. 2, the antennaassembly (201) is mounted in a low-profile radome. The radome can be aninherent part of the look and feel of the small cell base station (110),in this example the base station is mounted on a pole (210) which couldbe a utility pole or part of a building structure. Additionally, theantenna radome in this embodiment fictions as a solar shield to lowerthe temperature of the metal heat sink when it is exposed to directsunlight.

FIG. 3 is an embodiment of the antenna assembly of FIG. 2 illustratingcomponents of the antenna assembly. More specifically, FIG. 3illustrates the configuration of various components as would be visibleif an external radome were removed. The curved radome, shaped to meetthe aesthetic requirements of the design, covers a dielectric materialwith the same curved radius. As illustrated in FIG. 3, in between theradome and the dielectric numeral spacer are antenna radiator patches.Illustratively, the antenna radiator patches are configured to fit intothin pockets in the dielectric material which hold the patches in thecorrect location. Dielectric thickness varies based on particularfrequency and bandwidth. However, in this case the dielectric materialis about 9 mm thick for the 700 MHz band and 4 mm thick for the 2100 MHzband. This is the spacing between the aperture in the printed circuitmaterial and the radiating patch. A small pocket with the thickness of0.5 mm is cut out to hold the patch (typically 0.3 mm thick) in place.The patches themselves tend to be rectangular and of the order of onehalf wavelength of the radiating frequency given the effectivedielectric constant of the surrounding material. The conductive patchesare excited through apertures from the opposite side with 2 orthogonalelectric, field polarizations for each patch. Based on theconfiguration, each patch serves as an array element for 2 orthogonalantenna feeds.

In accordance with one aspect of an embodiment of the presentdisclosure, the receive frequency band for an LTE signal (1710-1755 MHz)is arrayed with two elements, (310) and (311). This provides array gainin the vertical direction while maintaining a desirable 70 degreeazimuth beamwidth. The 70 degree azimuth beamwidth provides a convenientbeam to support 3 sectors by placing 3 base stations at a singlelocation aimed in approximately 120 degrees from each other in a circle.In another aspect, the transmit frequency band for an LTE signal(2110-2155 MHz) is arrayed with two elements (320) and (321). In afurther aspect, a Wi-Fi signal frequency hand (unlicensed spectrum at2.4 GHz and 5 GHz) is arrayed with element (330) and (331).

In another embodiment of the invention, the unlicensed spectrum antennaelements are dual band. They resonate in both the 24 GHz and the 5 GHzunlicensed bands using a modified patch with 2 semi-circular slots cutout (330, 331). Notice that each technology has a similarcross-polarization scheme (+45 degrees and −45 degrees), and a similargain pattern in both the vertical and azimuth directions. This supportsat advantage of maintaining similar coverage patterns for multiple airinterface technologies in the base station so that the coverage can bemet easily with as few units as possible and in an efficient manner foreach technology. The cross polarization for each antenna supports 2transmit and 2 receive paths for each technology that can be used formultiple techniques such as 2×2 MIMO spatial multiplexing, transmit orreceive diversity, or transmit anchor receive beamforming according tothe capabilities and standard practices used in each of the supportedair interface technologies.

FIG. 4 is an embodiment of the antenna assembly of FIG. 2 illustrating areverse side of the antenna assembly. Illustratively, FIG. 4 illustratesas perspective in a portion of the antenna assembly that faces inwardstowards the metal housing. As illustrated in FIG. 4, the antennaassembly includes a radome, such as plastic radome (430), thatfunctions, at least in part, as a solar shield, environmentalprotections for the antenna, and a low-loss RF invisible window for theantenna. The radome may also function as a mechanical mounting point. Inan aspect of the design the antenna layers are built up structurallyfrom the radome and the radome itself contains the points to whichmechanical fasteners connect the entire assembly to the metal housing ofthe base station.

With continued reference to FIG. 4, a dielectric sheet (440) that actsas a precision mechanical spacer between the RF resonating and radiatingpatches, shown in FIG. 3 (310, 311, 320, 321, 330, and 331), and thedouble-sided printed circuit board (450) of low-loss microwavedielectric material containing a copper ground plane with slots (410) onone side and copper microstrip feed lines on the other side.Illustratively, exposed copper portions maybe covered with solder maskexcept the locations where the cables connections are soldered to theboard. The solder-mask facilitates moisture, protection for the antennafeeds. A coaxial cable is connected and the junction coated withwaterproofing material such as silicone. The coaxial cable and microwaveconnector permit the antenna to be used or disconnected so that analternate external coaxial cable leading to an alternate antenna can beconnected to the base station if desired. In that situation theintegrated antenna is left in place, disconnected, and continues toserve as a solar shield and aesthetic component of the design.

FIG. 5 illustrates an embodiment of small cell have station features tomate with and utilize an antenna assembly (430). Illustrative, theantenna assembly (430) may be shown as substantially transparent tovisualize at least a portion of housing structure underneath. In oneembodiment, the aluminum cooling fins (520) for the base station (110)are removed in the areas directly behind the apertures that feed each ofthe radiating patches. Such a configuration may enhance the antennaradiation pattern, improve the radiation efficiency, reduce the antennagain in the reverse direction, and provide cross-polar discriminationnecessary for multiple antenna performance. With continued reference toFIG. 5, the waterproof connectors (532) in the housing provide directand low-loss RF connection between the base station and the integratedantennas while permitting protection of the active electronics insidethe base station from environmental conditions.

FIG. 6 illustrates RF radiation patterns illustrative of usage of anantenna assembly. As illustrated in FIG. 6, the azimuth pattern is shownwith a representation of the base station (110) shown in the orientationin which the pattern is taken relative to the base station. The patternis shown for the +45′ polarization. In which case the +45° port showshigh efficiency and gain while the −45° port shows the isolation or XPD(cross-polar discrimination) which preferably has a very small response.In this case, a response that is lower by 10-15 dB provides sufficientisolation or decorrelation between the two polarizations so that it is asmall and insignificant proportion of the total correlation between thepolarizations. External sources of coupling between the polarizations,including the RE channel propagation model and the handset antennaperformance, will tend to provide at least −10 dB of correlation andwill dominate the base station antenna performance shown in FIG. 6.

It will be appreciated by those skilled in the art and others that allof the functions described in this disclosure may be embodied insoftware executed by one or more processors of the disclosed componentsand mobile communication devices. The software may be persistentlystored in any type of non-volatile storage.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment.

Any process descriptions, elements, or blocks in the flow diagramsdescribed herein and/or depicted in the attached figures should beunderstood as potentially representing modules, segments, or portions ofcode which include one or more executable instructions for implementingspecific logical functions or steps in the process. Alternateimplementations are included within the scope of the embodimentsdescribed herein in which elements or functions may be deleted, executedout of order from that shown or discussed, including substantiallyconcurrently or in reverse order, depending on the functionalityinvolved, as would be understood by those skilled in the art. It willfurther be appreciated that the data and/or components described abovemay be stored on a computer-readable medium and loaded into memory ofthe computing device using a drive mechanism associated with a computerreadable storing the computer executable components such as a CD-ROM,DVD-ROM, or network interface further, the component and/or data can beincluded in a single device or distributed in any manner. Accordingly,general purpose computing devices may be configured to implement theprocesses, algorithms, and methodology of the present disclosure withthe processing and/or execution of the various data and/or componentsdescribed above.

It should be emphasized that many variations and modifications may bemade to the above-described embodiments, the elements of which am to beunderstood as being among other acceptable examples. All suchmodifications and variations are intended to be included herein withinthe scope of this disclosure and protected by the following claims.

What is claimed is:
 1. An antenna assembly for use in a small cell basestation, the antenna assembly comprising: a curved radome to serve as ahousing and function as part of a solar shield; a dielectric materialwithin the curved radome and conforming with an interior shape of thecurved radome; and a plurality of antenna patches provided between thecurved radome and the dielectric material, each antenna patch configuredto serve as an array element for two orthogonal antenna feeds, whereineach of the antenna patches is configured to be excited with twoorthogonal field polarizations, wherein the antenna patches comprisepairs of antenna patches comprising a resonating patch and a radiatingpatch, wherein the dielectric material is configured to serve as aprecision mechanical spacer between the resonating patch and radiatingpatch of each of the pairs of the antenna patches, wherein a first pairof the antenna patches has dimensions for receiving and/or transmittingin a first Long Term Evolution (LTE) frequency band, wherein a secondpair of the antenna patches has dimensions for receiving and/ortransmitting in a second LTE frequency band, and wherein a third pair ofthe antenna patches has dimensions for receiving and transmitting in oneor more wireless local area network (WLAN) frequency bands.
 2. Theantenna assembly of claim 1 wherein the antenna patches are located inthin pockets of the dielectric material.
 3. The antenna assembly ofclaim 2 wherein the thin pockets are cutouts in the dielectric materialand configured to hold the antenna patches in predetermined positions.4. The antenna assembly of claim 3 wherein the dielectric material is adielectric sheet, and wherein the antenna patches are excited throughapertures within the dielectric sheet from a side opposite the radome.5. The antenna assembly of claim 1 wherein the third pair of antennapatches includes semi-circular cut outs for resonating in both a 2.4 GHzand a 5 GHz WLAN frequency band.
 6. An antenna assembly for use in asmall cell base station, the antenna assembly comprising: a curvedradome to serve as a housing and function as part of a solar shield; adielectric material within the curved radome and conforming with aninterior shape of the curved radome; and a plurality of antenna patchesprovided between the curved radome and the dielectric material, eachantenna patch configured to serve as an array element for two orthogonalantenna feeds, wherein each of the antenna patches is configured to beexcited with two orthogonal field polarizations, wherein the antennapatches comprise pairs of antenna patches comprising a resonating patchand a radiating patch, wherein the dielectric material is configured toserve as a precision mechanical spacer between the resonating patch andradiating patch of each of the pairs of the antenna patches, and whereineach of the pairs has a similar cross-polarization scheme and a similargain pattern in vertical and azimuth directions.
 7. The antenna assemblyof claim 6 wherein: a first pair of the antenna patches has dimensionsfor receiving in a first cellular frequency band, a second pair of theantenna patches has dimensions for transmitting in the first cellularfrequency band, a third pair of the antenna patches has dimensions forreceiving in a second cellular frequency band, a fourth pair of theantenna patches has dimensions for transmitting in the second cellularfrequency band, and a fifth pair of the antenna patches has dimensionsfor receiving and transmitting in one or more wireless local areanetwork (WLAN) frequency bands.
 8. The antenna assembly of claim 6wherein the antenna patches are located in thin pockets of thedielectric material.
 9. The antenna assembly of claim 8 wherein the thinpockets are cutouts in the dielectric material and configured to holdthe antenna patches in predetermined positions.
 10. The antenna assemblyof claim 9 wherein the dielectric material is a dielectric sheet, andwherein the antenna patches are excited through apertures within thedielectric sheet from a side opposite the radome.
 11. An antennaassembly for use in a small cell base station, the antenna assemblycomprising: a curved radome to serve as a housing and function as partof a solar shield; a dielectric material within the curved radome andconforming with an interior shape of the curved radome; and a pluralityof antenna patches provided between the curved radome and the dielectricmaterial, each antenna patch configured to serve as an array element fortwo orthogonal antenna feeds, wherein each of the antenna patches isconfigured to be excited with two orthogonal field polarizations,wherein the antenna patches comprise pairs of antenna patches comprisinga resonating patch and a radiating patch, wherein the dielectricmaterial is configured to serve as a precision mechanical spacer betweenthe resonating patch and radiating patch of each of the pairs of theantenna patches, and wherein at least some of the pairs of antennapatches are configured for 2×2 MIMO spatial multiplexing.
 12. Theantenna assembly of claim 11 wherein the antenna patches are located inthin pockets of the dielectric material.
 13. The antenna assembly ofclaim 12 wherein the thin pockets are cutouts in the dielectric materialand configured to hold the antenna patches in predetermined positions.14. The antenna assembly of claim 13 wherein the dielectric material isa dielectric sheet, and wherein the antenna patches are excited throughapertures within the dielectric sheet from a side opposite the radome.15. An antenna assembly for use in a small cell base station, theantenna assembly comprising: a curved radome to serve as a housing andfunction as part of a solar shield; a dielectric material within thecurved radome and conforming with an interior shape of the curvedradome; a plurality of antenna patches provided between the curvedradome and the dielectric material, each antenna patch configured toserve as an array element for two orthogonal antenna feeds; andremovable cooling fins provided behind the apertures, the cooling finsbeing removable from a side opposite the radome, wherein each of theantenna patches is configured to be excited with two orthogonal fieldpolarizations, wherein the antenna patches comprise pairs of antennapatches comprising a resonating patch and a radiating patch, and whereinthe dielectric material is configured to serve as a precision mechanicalspacer between the resonating patch and radiating patch of each of thepairs of the antenna patches.
 16. The antenna assembly of claim 15wherein the antenna patches are located in thin pockets of thedielectric material.
 17. The antenna assembly of claim 16 wherein thethin pockets are cutouts in the dielectric material and configured tohold the antenna patches in predetermined positions.
 18. The antennaassembly of claim 17 wherein the dielectric material is a dielectricsheet, and wherein the antenna patches are excited through apertureswithin the dielectric sheet from a side opposite the radome.